The present invention is directed to an imaging process. More specifically, the present invention is directed to a ballistic aerosol marking process using specific marking materials. One embodiment of the present invention is directed to a process for depositing marking material onto a substrate which comprises (a) providing a propellant to a head structure, said head structure having at least one channel therein, said channel having an exit orifice with a width no larger than about 250 microns through which the propellant can flow, said propellant flowing through the channel to form thereby a propellant stream having kinetic energy, said channel directing the propellant stream toward the substrate, and (b) controllably introducing a particulate marking material into the propellant stream in the channel, wherein the kinetic energy of the propellant particle stream causes the particulate marking material to impact the substrate, and wherein the particulate marking material comprises toner particles which comprise a vinyl resin, an optional colorant, and poly(3,4-ethylenedioxythiophene), said toner particles having an average particle diameter of no more than about 10 microns and a particle size distribution of GSD equal to no more than about 1.25, wherein said toner particles are prepared by an emulsion aggregation process, said toner particles having an average bulk conductivity of at least about 10xe2x88x9211 Siemens per centimeter.
Ink jet is currently a common printing technology. There are a variety of types of ink jet printing, including thermal ink jet printing, piezoelectric ink jet printing, and the like. In ink jet printing processes, liquid ink droplets are ejected from an orifice located at one terminus of a channel. In a thermal ink jet printer, for example, a droplet is ejected by the explosive formation of a vapor bubble within an ink bearing channel. The vapor bubble is formed by means of a heater, in the form of a resistor, located on one surface of the channel.
Several disadvantages can be associated with known ink jet systems. For a 300 spot-per-inch (spi) thermal ink jet system, the exit orifice from which an ink droplet is ejected is typically on the order of about 64 microns in width, with a channel-to-channel spacing (pitch) of typically about 84 microns; for a 600 dpi system, width is typically about 35 microns and pitch is typically about 42 microns. A limit on the size of the exit orifice is imposed by the viscosity of the fluid ink used by these systems. It is possible to lower the viscosity of the ink by diluting it with increasing amounts of liquid (such as water) with an aim to reducing the exit orifice width. The increased liquid content of the ink, however, results in increased wicking, paper wrinkle, and slower drying time of the ejected ink droplet, which negatively affects resolution, image quality (such as minimum spot size, intercolor mixing, spot shape), and the like. The effect of this orifice width limitation is to limit resolution of thermal ink jet printing, for example to well below 900 spi, because spot size is a function of the width of the exit orifice, and resolution is a function of spot size.
Another disadvantage of known ink jet technologies is the difficulty of producing grayscale printing. It is very difficult for an ink jet system to produce varying size spots on a printed substrate. If one lowers the propulsive force (heat in a thermal ink jet system) so as to eject less ink in an attempt to produce a smaller dot, or likewise increases the propulsive force to eject more ink and thereby to produce a larger dot, the trajectory of the ejected droplet is affected. The altered trajectory in turn renders precise dot placement difficult or impossible, and not only makes monochrome grayscale printing problematic, it makes multiple color grayscale ink jet printing impracticable. In addition, preferred grayscale printing is obtained not by varying the dot size, as is the case for thermal ink jet, but by varying the dot density while keeping a constant dot size.
Still another disadvantage of common ink jet systems is rate of marking obtained. Approximately 80 percent of the time required to print a spot is taken by waiting for the ink jet channel to refill with ink by capillary action. To a certain degree, a more dilute ink flows faster, but raises the problem of wicking, substrate wrinkle, drying time, and the like, discussed above.
One problem common to ejection printing systems is that the channels may become clogged. Systems such as thermal ink jet which employ aqueous ink colorants are often sensitive to this problem, and routinely employ non-printing cycles for channel cleaning during operation. This cleaning is required, since ink typically sits in an ejector waiting to be ejected during operation, and while sitting may begin to dry and lead to clogging.
Ballistic aerosol marking processes overcome many of these disadvantages. Ballistic aerosol marking is a process for applying a marking material to a substrate, directly or indirectly. In particular, the ballistic aerosol marking system includes a propellant which travels through a channel, and a marking material that is controllably (i.e., modifiable in use) introduced, or metered, into the channel such that energy from the propellant propels the marking material to the substrate. The propellant is usually a dry gas that can continuously flow through the channel while the marking apparatus is in an operative configuration (i.e., in a power-on or similar state ready to mark). Examples of suitable propellants include carbon dioxide gas, nitrogen gas, clean dry ambient air, gaseous products of a chemical reaction, or the like; preferably, nonoxic propellants are employed, although in certain embodiments, such as devices enclosed in a special chamber or the like, a broader range of propellants can be tolerated. The system is referred to as xe2x80x9cballistic aerosol markingxe2x80x9d in the sense that marking is achieved by in essence launching a non-colloidal, solid or semi-solid particulate, or alternatively a liquid, marking material at a substrate. The shape of the channel can result in a collimated (or focused) flight of the propellant and marking material onto the substrate.
The propellant can be introduced at a propellant port into the channel to form a propellant stream. A marking material can then be introduced into the propellant stream from one or more marking material inlet ports. The propellant can enter the channel at a high velocity. Alternatively, the propellant can be introduced into the channel at a high pressure, and the channel can include a constriction (for example, de Laval or similar converging/diverging type nozzle) for converting the high pressure of the propellant to high velocity. In such a situation, the propellant is introduced at a port located at a proximal end of the channel (the converging region), and the marking material ports are provided near the distal end of the channel (at or further down-stream of the diverging region), allowing for introduction of marking material into the propellant stream.
In the situation where multiple ports are provided, each port can provide for a different color (for example, cyan, magenta, yellow, and black), pre-marking treatment material (such as a marking material adherent), post-marking treatment material (such as a substrate surface finish material, for example, matte or gloss coating, or the like), marking material not otherwise visible to the unaided eye (for example, magnetic particle-bearing material, ultraviolet-fluorescent material, or the like) or other marking material to be applied to the substrate. Examples of materials suitable for pre-marking treatment and post-marking treatment include polyester resins (either linear or branched); poly(styrenic) homopolymers; poly(acrylate) and poly(methacrylate) homopolymers and mixtures thereof; random copolymers of styrenic monomers with acrylate, methacrylate, or butadiene monomers and mixtures thereof; polyvinyl acetals; poly(vinyl alcohol)s; vinyl alcohol-vinyl acetal copolymers; polycarbonates; mixtures thereof; and the like. The marking material is imparted with kinetic energy from the propellant stream, and ejected from the channel at an exit orifice located at the distal end of the channel in a direction toward a substrate.
One or more such channels can be provided in a structure which, in one embodiment, is referred to herein as a printhead. The width of the exit (or ejection) orifice of a channel is typically on the order of about 250 microns or smaller, and preferably in the range of about 100 microns or smaller. When more than one channel is provided, the pitch, or spacing from edge to edge (or center to center) between adjacent channels can also be on the order of about 250 microns or smaller, and preferably in the range of about 100 microns or smaller. Alternatively, the channels can be staggered, allowing reduced edge-to-edge spacing. The exit orifice and/or some or all of each channel can have a circular, semicircular, oval, square, rectangular, triangular or other cross-sectional shape when viewed along the direction of flow of the propellant stream (the channel""s longitudinal axis).
The marking material to be applied to the substrate can be transported to a port by one or more of a wide variety of ways, including simple gravity feed, hydrodynamic, electrostatic, ultrasonic transport, or the like. The material can be metered out of the port into the propellant stream also by one of a wide variety of ways, including control of the transport mechanism, or a separate system such as pressure balancing, electrostatics, acoustic energy, ink jet, or the like.
The marking material to be applied to the substrate can be a solid or semi-solid particulate material, such as a toner or variety of toners in different colors, a suspension of such a marking material in a carrier, a suspension of such a marking material in a carrier with a charge director, a phase change material, or the like. Preferably the marking material is particulate, solid or semi-solid, and dry or suspended in a liquid carrier. Such a marking material is referred to herein as a particulate marking material. A particulate marking material is to be distinguished from a liquid marking material, dissolved marking material, atomized marking material, or similar non-particulate material, which is generally referred to herein as a liquid marking material. However, ballistic aerosol marking processes are also able to utilize such a liquid marking material in certain applications.
Ballistic aerosol marking processes also enable marking on a wide variety of substrates, including direct marking on non-porous substrates such as polymers, plastics, metals, glass, treated and finished surfaces, and the like. The reduction in wicking and elimination of drying time also provides improved printing to porous substrates such as paper, textiles, ceramics, and the like. In addition, ballistic aerosol marking processes can be configured for indirect marking, such as marking to an intermediate transfer member such as a roller or belt (which optionally can be heated), marking to a viscous binder film and nip transfer system, or the like.
The marking material to be deposited on a substrate can be subjected to post-ejection modification, such as fusing or drying, overcoating, curing, or the like. In the case of fusing, the kinetic energy of the material to be deposited can itself be sufficient effectively to melt the marking material upon impact with the substrate and fuse it to the substrate. The substrate can be heated to enhance this process. Pressure rollers can be used to cold-fuse the marking material to the substrate. In-flight phase change (solid-liquid-solid) can alternatively be employed. A heated wire in the particle path is one way to accomplish the initial phase change. Alternatively, propellant temperature can accomplish this result. In one embodiment, a laser can be employed to heat and melt the particulate material in-flight to accomplish the initial phase change. The melting and fusing can also be electrostatically assisted (i.e., retaining the particulate material in a desired position to allow ample time for melting and fusing into a final desired position). The type of particulate can also dictate the post-ejection modification. For example, ultraviolet curable materials can be cured by application of ultraviolet radiation, either in flight or when located on the material-bearing substrate.
Since propellant can continuously flow through a channel, channel clogging from the build-up of material is reduced (the propellant effectively continuously cleans the channel). In addition, a closure can be provided that isolates the channels from the environment when the system is not in use. Alternatively, the printhead and substrate support (for example, a platen) can be brought into physical contact to effect a closure of the channel. Initial and terminal cleaning cycles can be designed into operation of the printing system to optimize the cleaning of the channel(s). Waste material cleaned from the system can be deposited in a cleaning station. It is also possible, however, to engage the closure against an orifice to redirect the propellant stream through the port and into the reservoir thereby to flush out the port.
Further details on the ballistic aerosol marking process are disclosed in, for example, Copending U.S. application Ser. No. 09/163,893, filed Sep. 30, 1998, with the named inventors Gregory B. Anderson, Steven B. Bolte, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, Jaan Noolandi, Joel A. Kubby, Eric Peeters, Raj B. Apie, Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cBallistic Aerosol Marking Apparatus for Marking a Substrate,xe2x80x9d Copending U.S. application Ser. No. 09/164,124, filed Sep. 30, 1998, with the named inventors Gregory B. Anderson, Steven B. Bolte, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, Joan Noolandi, Joel A. Kubby, Eric Peeters, Raj B. Apte, Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cMethod of Marking a Substrate Employing a Ballistic Aerosol Marking Apparatus,xe2x80x9d Copending U.S. application Ser. No. 09/164,250, filed Sep. 30, 1998, with the named inventors Gregory B. Anderson, Danielle C. Boils, Steven B. Bolte, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, T. Brian McAneney, Maria N. V. McDougall, Karen A. Moffat, Joan Noolandi, Richard P. N. Veregin, Paul D. Szabo, Joel A. Kubby, Eric Peeters, Raj B. Apte, Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cBallistic Aerosol Marking Apparatus for Treating a Substrate,xe2x80x9d Copending U.S. application Ser. No. 09/163,808, filed Sep. 30, 1998, with the named inventors Gregory B. Anderson, Danielle C. Boils, Steven B. Bolte, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, T. Brian McAneney, Maria N. V. McDougall, Karen A. Moffat, Joan Noolandi, Richard P. N. Veregin, Paul D. Szabo, Joel A. Kubby, Eric Peeters, Raj B. Apte. Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cMethod of Treating a Substrate Employing a Ballistic Aerosol Marking Apparatus,xe2x80x9d Copending U.S. application Ser. No. 09/163,765, filed Sep. 30, 1998, with the named inventors Gregory B. Anderson, Steven B. Bolte, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, Joan Noolandi, Joel A. Kubby, Eric Peeters, Raj B. Apte, Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cCartridge for Use in a Ballistic Aerosol Marking Apparatus,xe2x80x9d Copending U.S. application Ser. No. 09/163,839, filed Sep. 30, 1998, with the named inventors Abdul M. Elhatem, Dan A. Hays, Joan Noolandi, Kaiser H. Wong, Joel A. Kubby, Tuan Anh Vo, and Eric Peeters, entitled xe2x80x9cMarking Material Transport,xe2x80x9d Copending U.S. application Ser. No. 09/163,954, filed Sep. 30, 1998, with the named inventors Gregory B. Anderson, Andrew A. Berlin, Steven B. Bolte, Ga Neville Connell, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, Jaan Noolandi, Joel A. Kubby, Eric Peeters, Raj B. Apte, Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cBallistic Aerosol Marking Apparatus for Marking with a Liquid Material,xe2x80x9d Copending U.S. application Ser. No. 09/163,924, filed in Sep. 30, 1998, with the named inventors Gregory B. Anderson, Andrew A. Berlin, Steven B. Bolte, Ga Neville Connell, Dan A. Hays, Warren B. Jackson, Gregory J. Kovacs, Meng H. Lean, Joan Noolandi, Joel A. Kubby, Eric Peeters, Raj B. Apte, Philip D. Floyd, An-Chang Shi, Frederick J. Endicott, Armin R. Volkel, and Jonathan A. Small, entitled xe2x80x9cMethod for Marking with a Liquid Material Using a Ballistic Aerosol Marking Apparatus,xe2x80x9d Copending U.S. application Ser. No. 09/163,825, filed Sep. 30, 1998, with the named inventor Kaiser H. Wong, entitled xe2x80x9cMulti-Layer Organic Overcoat for Electrode Grid,xe2x80x9d Copending U.S. application Ser. No. 09/164,104, filed Sep.30, 1998, with the named inventors T. Brian McAneney, Joan Noolandi, and An-Chang Shi. entitled xe2x80x9cKinetic Fusing of a Marking Material,xe2x80x9d U.S. application Ser. No. 09/163,904 (now U.S. Pat. No. 6,116,718), filed Sep. 30, 1998, with the named inventors Meng H. Lean, Joan Noolandi, Eric Peeters, Raj B. Apte, Philip D. Floyd, and Armin R. Volkel, entitled xe2x80x9cPrint Head for Use in a Ballistic Aerosol Marking Apparatus,xe2x80x9d Copending application U.S. Ser. No. 09/163,799, filed Sep. 30, 1998, with the named inventors Meng H. Lean, Jaan Noolandi, Eric Peeters, Raj B. Apte, Philip D. Floyd, and Armin R. Volkel, entitled xe2x80x9cMethod of Making a Print Head for Use in a Ballistic Aerosol Marking Apparatus,xe2x80x9d Copending U.S. application Ser. No. 09/163,664, filed Sep. 30, 1998, with the named inventors Bing R. Hsieh, Kaiser H. Wong, and Tuan Anh Vo, entitled xe2x80x9cOrganic Overcoat for Electrode Grid,xe2x80x9d and Copending U.S. application Ser. No. 09/163,518, filed Sep. 30, 1998, with the named inventors Kaiser H. Wong and Tuan Anh Vo, entitled xe2x80x9cInorganic Overcoat for Particulate Transport Electrode Gridxe2x80x9d, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 5,834,080 (Mort et al.), the disclosure of which is totally incorporated herein by reference, discloses controllably conductive polymer compositions that may be used in electrophotographic imaging developing systems, such as scavengeless or hybrid scavengeless systems or liquid image development systems. The conductive polymer compositions includes a charge-transporting material (particularly a charge-transporting, thiophene-containing polymer or an inert elastomeric polymer, such as a butadiene- or isoprene-based copolymer or an aromatic polyether-based polyurethane elastomer, that additionally comprises charge transport molecules) and a dopant capable of accepting electrons from the charge-transporting material. The invention also relates to an electrophotographic printing machine, a developing apparatus, and a coated transport member, an intermediate transfer belt, and a hybrid compliant photoreceptor comprising a composition of the invention.
U.S. Pat. No. 5,853,906 (Hsieh), the disclosure of which is totally incorporated herein by reference, discloses a conductive coating comprising an oxidized oligomer salt, a charge transport component, and a polymer binder, for example, a conductive coating comprising an oxidized tetratolyidiamine salt of the formula 
a charge transport component, and a polymer binder, wherein X- is a monovalent anion.
U.S. Pat. No. 5,457,001 (Van Ritter), the disclosure of which is totally incorporated herein by reference, discloses an electrically conductive toner powder, the separate particles of which contain thermoplastic resin, additives conventional in toner powders, such as coloring constituents and possibly magnetically attractable material, and an electrically conductive protonized polyaniline complex, the protonized polyaniline complex preferably having an electrical conductivity of at least 1 S/cm, the conductive complex being distributed over the volume of the toner particles or present in a polymer-matrix at the surface of the toner particles.
U.S. Pat. No. 5,202,211 (Vercoulen et al.), the disclosure of which is totally incorporated herein by reference, discloses a toner powder comprising toner particles which carry on their surface and/or in an edge zone close to the surface fine particles of electrically conductive material consisting of fluorine-doped tin oxide. The fluorine-doped tin oxide particles have a primary particle size of less than 0.2 micron and a specific electrical resistance of at most 50 ohms.meter. The fluorine content of the tin oxide is less than 10 percent by weight, and preferably is from 1 to 5 percent by weight.
U.S. Pat. No. 5,035,926 (Jonas et al.), the disclosure of which is totally incorporated herein by reference, discloses new polythiophenes containing structural units of the formula 
in which A denotes an optionally substituted C1-C4 alkylene radical, their preparation by oxidative polymerization of the corresponding thiophenes, and the use of the polythiophenes for imparting antistatic properties on substrates which only conduct electrical current poorly or not at all, in particular on plastic mouldings, and as electrode material for rechargeable batteries.
While known compositions and processes are suitable for their intended purposes, a need remains for improved marking processes. In addition, a need remains for improved ballistic aerosol marking materials and processes. Further, a need remains for ballistic aerosol marking materials and processes that enable the printing of very small pixels, enabling printing resolutions of 900 dots per inch or more. Additionally, there is a need for ballistic aerosol marking materials and processes in which the possibility of the marking material clogging the printing channels is reduced. There is also a need for ballistic aerosol marking processes wherein the marking material does not become undesirably charged. In addition, there is a need for ballistic aerosol marking processes wherein the marking material exhibits desirable flow properties. Further, there is a need for ballistic aerosol marking processes wherein the marking material contains particles of desirably small particle size and desirably narrow particle size distribution. Additionally, there is a need for ballistic aerosol marking processes wherein the marking material can obtain a low degree of surface charge without becoming so highly charged that the material becomes agglomerated or causes channel clogging. A need also remains for ballistic aerosol marking processes wherein the marking material is semi-conductive or conductive (as opposed to insulative) and capable of retaining electrostatic charge. In addition, a need remains for ballistic aerosol marking processes wherein the marking materials have sufficient conductivity to provide for inductive charging to enable toner transport and gating into the printing channels. Further, a need remains for ballistic aerosol marking processes wherein the marking materials can be selected to control the level of electrostatic charging and conductivity, thereby preventing charge build up in the BAM subsystems, controlling relative humidity, and maintaining excellent flow. Additionally, a need remains for ballistic aerosol marking processes wherein the marking materials have desirably low melting temperatures. There is also a need for ballistic aerosol marking processes wherein the marking materials have tunable melt and gloss properties, wherein the same monomers can be used to generate marking materials that have different melt and gloss characteristics by varying polymer characteristics such as molecular weight (Mw, Mn, MWD, or the like) or crosslinking. In addition, there is a need for ballistic aerosol marking processes wherein the marking materials have desirable glass transition temperatures for enabling efficient transfer of the marking material from an intermediate transfer or transfuse member to a print substrate. Further, there is a need for ballistic aerosol marking processes wherein the marking materials have desirable glass transition temperatures for enabling efficient transfer of the marking material from a heated intermediate transfer or transfuse member to a print substrate. Additionally, there is a need for ballistic aerosol marking processes wherein the marking materials have a wide range of colors with desirable color characteristics. A need also remains for ballistic aerosol marking processes wherein the marking materials exhibit good transparency characteristics. In addition, a need remains for ballistic aerosol marking processes wherein the marking materials exhibit good fusing performance. Further, a need remains for ballistic aerosol marking processes wherein the marking material forms images with low toner pile heights, even for full color superimposed images. Additionally, a need remains for ballistic aerosol marking processes wherein the marking material comprises a resin particle encapsulated with a conductive polymer, wherein the conductive polymer is chemically bound to the particle surface. There is also a need for ballistic aerosol marking processes wherein the marking material comprises particles that have tunable morphology in that the particle shape can be selected to be spherical, highly irregular, or the like.
The present invention is directed to a process for depositing marking material onto a substrate which comprises (a) providing a propellant to a head structure, said head structure having at least one channel therein, said channel having an exit orifice with a width no larger than about 250 microns through which the propellant can flow, said propellant flowing through the channel to form thereby a propellant stream having kinetic energy, said channel directing the propellant stream toward the substrate, and (b) controllably introducing a particulate marking material into the propellant stream in the channel, wherein the kinetic energy of the propellant particle stream causes the particulate marking material to impact the substrate, and wherein the particulate marking material comprises toner particles which comprise a vinyl resin, an optional colorant, and poly(3,4-ethylenedioxythiophene), said toner particles having an average particle diameter of no more than about 10 microns and a particle size distribution of GSD equal to no more than about 1.25, wherein said toner particles are prepared by an emulsion aggregation process, said toner particles having an average bulk conductivity of at least about 10xe2x88x9211 Siemens per centimeter.